Servo-motor damping assembly



Dec. 22, 1964 J. R. PATMORE ETAL 3,162,274

SERVO-MOTOR DAMPING ASSEMBLY 2 Sheets-Sheet 1 Filed Oct. 30, 1962 u Lmhl1N VEN 1 ORS JAMES R. PATMORE HARRY A. WlLLIAMSON Dec. 22, 1964 J. R.PArMoRE ETAL 3,162,274

SERVO-MOTOR DAMPING ASSEMBLY 2 Sheets-Sheet 2 Filed OCT.. 50, 1952`TAR/IES R. PATMORE HARFQY A WILLIAMSON m. ma

ATTORNEY United States Patent O 3,162,274 SERVO-MTR DAlw/l'iliellASSEMBLY James R. Patmore, Neptune, and Harry A. Williamson, Red Bank,NJ., assignors to Electronic Assoeiates inc., Long Branch, NJ., acorporation of New Jersey Filed Utet. 3i), i962, Ser. No. 234.186 lilClaims. (Cl. iSd-90) This invention relates to a servo-motor and inparticular is directed to a small servo-motor tted with a dampingelement for developing a variable damping factor.

Servo-motors are widely used in a variety of applications and variousmeans are known for stabilizing servo mechanisms an dtake ya variety ofdifferent forms. rhe form `of stabilizing means may be purely electricalin nature, such as the weil known lead network; or it may be purelymechanical in nature, such as the well known friction damper; or it maybe a combination of mechanical and electrical means, such as a dragelement disposed for rotation in a variable iiux field. Each known typeof stabilizing means has one or more desirable characteristics, but eachis also possessed with a general inability either of developing aVariable damping factor or of developing such a variable damping factorwithout signicant sacrifices in cost or size.

One application where it is essential to provide variable damping is inthe field of data reduction where input data is to be presentedgraphically in the forrn of either points or lines. in such application,the line data is usually presented to the typical servo systems drivingthe pen and arm of an X-Y recorder. The pen o-r stylus of the recorderis in continuous engagement with a plotting surface and a graphicalrepresentation of the input data is produced continuously. The inputsignals are usually continuous and of continuously varying amplitude.Point data is usually obtained from magnetic tape, punched cards,punched tapes or the like in a suitable digital form for feeding intothe recorder where the information is converted into analog signals forapplication to the servo motors.V In point plotting, the pen or stylusengages the plotting surface only after the servo motors null andaccordingly the rapid and accurate nulling of the servo motor increasesthe amount of data which can be processed and reduced to graphical form.

The damping requirements for these two applications are quite diverseand until the present invention, a single damping element of reasonablesize and cost which would permit maximum acceleration and minimum delaytime form of graph plotting to another form with an accompanying changeto the corresponding type of dam in.

The single An object of this invention is to combine a viscous and EhZMPatented Dec. 22, 1984 lCe.

The preferred embodiment of the present invention is characterized byviscous damping means in the form of a plurality of discs ysecured to aservo motor shaft for rotation therewith and cooperating in interfacerelationship with a like plurality of discs fixed to a casing which isrotatably mounted on the shaft; all the discs are submerged in a volumeof oil of suitable viscosity to form a fluid couple whereby an inertialelement fixed to the exterior of the casing for rotation therewithprovides the servo motor shaft with viscous coupled inertial damping. Alatching device is operated to prevent the rotation of the inertialelement and the casing so that the servo motor shaft may be operatedwith only viscous damping.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodiment ofthe invention taken in connection with the accompanying drawing,wherein:

PEG. 1 is an end view of a servo motor embodying the invention;

FIG. 2 is a partial section view, taken substantially along the line 2 2of FIG. l, and including the end latching device;

FIG. 3 is a partial section view taken along the line 3-3 of FG. l; and

FIG. 4 is a section view along the line 4-4 of FG. 2.

Referring now to FIG. 2, the preferred embodiment of the presentinvention includes a servo motor 10 with the usual rotatable shaft 12which includes an output shaft end jtd. Suitable gearing 16 couples theoutput shaft end 14 to a driven element iS that is part of the pen armand stylus assembly of the graphic recorder (not shown). The shaft l2also includes an opposite shaft end 20 to which a combined viscous andinertial damping assembly is attached.

A plurality of disc elements 22 are secured to the shaft v 2l) in axialspaced relation by any suitable means whereby the discs 2?. and shaft2t) are rotated as a unit. A casing 2,4 surrounds the discs 22 and ismounted on shaft 2t) by means of annular bearing seals 26-28 disposed onopposite ends of the shaft discs 22 to permit rotation of the rotationof the casing 24 relative to the shaft 2t). A second plurality of discelements 3l) are axially spaced and at their outer peripheries are fixedtothe rotatable casing 24. The discs 39 extend into the spaces betweenthe discs 22 and a liquid suitably viscous is contained with the casing24; the liquid cooperates with the interfaces of the discs 22 and 314ito form a fluid coupling in which rotation of the discs 2,2 causesrotation of the discs 3i?.

A cup-shaped inertial element 32 of a desired mass is secured to theexterior of casing 24 as by bolts 3d extending through ti e bottom wallof inertial element 32 and being threaded through the casing 24. As isapparent from PEG. l, the bolts 3d also provide the means for securingthe discs 3@ to the casing 24 so that the inertial element 32, discs 3d,and casing 24 rotate as a unit. The cup-shaped inertial element 32comprises an outer portion 36, which substantially surrounds the outerperiphery of casing 24, and a bottom wall portion 322 which engages theaxial end wali of the casing 24. The annular periphery iii of the bottomwall portion 38 has an outer diameter that isless than that of the outerportion 36 so as to be radially offset therefrom.

The entire damping assembly is enclosed within a circular housing t2that is attached to the end of the servo motor i@ as by bolts 44. As isillustrated in FIG. 2, theV open end of housing ft2 is closed by a plate46 and any suitable' fastening` means. The plate de includes an annuvlarextension 4S disposed inwardly of the housing i2 and a substantiallysemicircular projection 50 disposed outwardly thereof. The extension 4-3is formed with a pair of diametrically opposed slots 51, each of whichslidably receives a latching element 52.- Each latching element 52 `biasof coil spring 62.

is provided with an arcuate latchV bar 53 juxtaposed the inertialelements periphery 4t? and a perpendicular arm 54 extending radiallyinwardly .and terminating in a semicircular abutment 561; eachg arm 54has a centrallylocated pin 58 extending' 'in-a `direction away Vfrom thelatch bar`r` 53 so as to be. ,positioned in an elongated recessed formedinthe platel projection 50.' A coil spring 62 is ydisposed in the recess60 `and is v'mounted in tension between the two latch pins S wherebythe. two latchingelements 52 are. biased towards eachother.

As is illustrated in FIG. 4, lthe latching elements 52.V

are forced radially outwardly `by means of. a latch key ed which has apair of bevelled surfaces66 to cooperate with The coilspring 62 maybedesigned to exert a larger or smaller biasing force kas required by theparticular installation; 'egg., a larger force would be needed for anas- Y sembly using a larger inertial mass to be damped by more than twolatching elements, and a smaller force wouldsuffice to lock asmallerinertial. mass. spring 62 also precludes accidental movement of thelatching arms 54 by the latch key 64 since its 'biasing force issufliciently large to resist a slight. ,push on ythe latch key 64 asvmay occur by accident; Thus, the coil-spring 62 in cooperation with therounded abutment 56 andV camming edges 66 functions as afdetent inVrequiring an initial force the abutment '56 .in camming the. latchingelements out- 'Y wardly against the bias of coil spring 62. Alongitudinal slot 68 inthe latch key -64 cooperates `witha-g-uide stoppin T70 which extends inwardly from the plate projection 5). The ylatchkey '64' is manually moved relative zto the pin 79 'by aperpendiculartab 72j on its free end. ..The

latc'harrns .'54, and the `latch key 64 sliderelative to the `innerlsurface. of plate 46 and such movement Vis guided by a retaining plate74 (FIG. 3) secured tothe inner surface as by the fourcircumferentially'spaced screwsl76.

' The following description of the sequence ofl operation will bedirected first to the operationwhere the pen assembly is to plota seriesof points on the ,graph paper yof the recorder. In point plotting, therecorder pen engages the graph paperonly after the servo motor nullswhich is best accomplished by providing the servo motor shaft withviscous damping only.

Inaccordance with the present invention, viscous dampof substantialmagnitude to push lthe latch key`64inward. ln line plotting,l theArecorder penrengages the graph ypaper `during the pen travel. in.response to `servo-motor operation `which' is best accomplished byproviding the servo motorV shaft with combined viscous and inertialdamping. The presentinvention. facilitates a rapid conversion from apoint. .plotting operation to a lineplotting operation even thoughythesame servo motor and recorder apparatus yare used. yCombined fviscous and inertial damping -is obtained by the simple,v singleoperationof the latch key 6. By manually .pushingV on the finger grip72,

Vthe latch key 64 slides radially inwardly towards .the lonv gitudinalaxis o f the assembly as viewed in FIG. 4. Such Vinward movement causesthe camming edges v66 to cam the rounded abutments 56 outwardly whereby`the latching ing is easily obtained ybyfolperation or ,the 'latch key64. By manually pulling on the 'finger grip 72, the latch key f 64slides rapidly outwardly from theaxis of the assembly as vviewed in FIG.4. Outward movement ofthe key 6.4

edges 56 of the latching arms 54 whereby the'latching elements 52 aremoved inwardly toward each other by the During such movement, -each .pin53 of each latch arm slides in its slot 6l' in the plate to' guide themovement of each latching arm 54. .The

latch bars 53am thus biased inwardly to clamp .the adjacentportions ofperiphery all and lock the'i'nertial element 32 against rotation.Inasmuch as thelcasingf-Zdand:v

the discs 3th are fixed tothe inerti-al element 32, ythe entireinertial'Y damping `assembly is stationary'evenlhough Vthe shaft 2) is,rotating. Y

The data for thepointplbts, which mayf-beobtained l from.. punched cardsor tape, are .converted Vto :analog signals that. cause rotation of theservo motor shaftZ.

drag of the .viscous fluid between the interfaces of the rotatingdiscs`22 and the'xed discs 3) causes arviscousv damping of therotation'of the shaft 20 'with the lresult that servo motor shaft 2).isaccurately and rapidly nulled. It should be. noted that .evenif therotation of the servo motor shaft A2i) should beaccompaniedwithinaccuracies during acceleration, deceleration or.velocity, suchinaccuracies are. rendered immaterialby the present invention Y because-the only.importantcharacteristic is thenull positionin .which the pointislplotted bythe pen assembly.

. 35 moves its cammingfedges 65. from contact with .the arcuate 5o Whenthe angular velocity` of theshaft 20 is reduced, the

for a particular input signal.- f present invention, the rotationofr'theservo motor-shaft is elements 52 are moved rapidlyoutwardlyagainst the the casing discs 3) causesthe inertial member 32rtorotate.

with theshaft 20. However,-wh'en thegangular. velocity ofthe shaft is:reduced or itsdirection of rotation isreversed, thevdrag of the viscousuid between'the interfaces of the discs 22 `and 30 effects a viscous:damping Vofthe Y rotation ofthe servo motor shaft 2li, and the.inertia` of .the

inertial -member 32 effects an inertial damping of such shaft rotation.In thefeventV therotation 'of the servo motor shaft vis accompanied by.any inaccuracies during .acceleration or deceleration,suchfinaccuracies are not material Abecause the only importantcharacteristic is the velocity which influences the distance ofthe pentravel In accordance with ythe rend/ered. substantially Vfree ofvelocity errors since the combinedpviscous yand inertial damping assuresaccurate 'response of the servo motor shaft 'to' the input signal.

` Nfl/hen the latch. key 64 is in the Vinward position as shown in FIG.4, the rounded'abutments 56 are biasedinto Y eng-agement with oppositeedges `of the vlatch tkey 64 and When the latch key 64 -isin thevoutward position, the k l rounded abutmentse on the-,two latchingelements 52de,

limited'by the engagement of thearcuate latch bars 53 on not engageeach.otherrbecause theiry inward movement is fl Vv the .inertial elementsurface zei); With such'an, arrangement, the biasing forceofceilysp'rirlg62 is'entirely:ldap-sv plied VVtothelatchfbars 53 whicharethus-,provided-witlraVA substantial clampingforce so-thatfthereis no`slippingvbe- 'i tween vvthe surfaced!) 'and the/latch 4bars Y53.Thisnonslipping vfeature -is .apparent since thelatchinggassembly ismanually positioned before operation oftherservo motor; i.e., theinertial element 32 is, locked-.in place anddoes not` VYaccelerate.- asfthe -servo n1otor..sliaft20fis increasing its]V sularvloity from zere inresponse-teauinput signal.

- thus friction-ally lock` the 'latch key 6ft. from accidental outwardmovement. Y

' The above described .damping `assembly constitutes a versatile. devicevwhich isquicklygconverted toV 'form a'first or a second type ofydamping-and VWhich'is readily adapted for'otherseryosystems merely bychanging the Viscosity of the fluid and/orY the number ofcooperatingxdiscs 22' 'and 30. inasmuch as many otherl changes could :bemade .am the above construction and many Aapparently widely.

diirerentv embodiments of 'the 'present inventioncould be made withoutAdepartingfrom-.the scope.thereof, itis' inf f tendedthat allmatter-.contained in theabove description Vor shown on the accompanyingdrawings shallbe inten' Y pretedga'sillustrative vandfnot'in alimitingsense. 7 Y

.Whatis'claimed is: r Y a, 1. .In a servo-motor, mechanism, the'.combinati'n compil-ising j 'rotartableshaft;-A

The coil.

output means connected to said shaft and adapted to record data fed to aservo motor,

a casing rotatably connected to said shaft and containing a volume ofiluid,

duid damping means secured to said shaft and extending into said casingfor viscous damping of said shaft during its rotation, and

an inertial element secured to said casing for rotation therewithwhereby viscous damping of said shaft is oombned with inertial dampingof said shaft during rotation thereof.

2. ln a servo-motor mechanism for a recorder or the like, thecombination comprising a rotatable shaft, output means connected to saidshaft adapted to record data fed to ak servo-motor, a casing rotatablymounted on said shaft and containing a volume of fluid, disc means fixedto said shaft and extending into said casing to form viscous dampingmeans for said shaft, an inertial element secured to said casing forrotation therewith whereby the viscous damping means is combined withinertial damping means during rotation Vof said shaft.

3. In combination with a servo-motor having a shaft, a viscous andinertial damping assembly comprising: a plurality of discs ixedlysecured to the servo-motor shaft, a casing rotatably mounted on theshaft, said easinr carrying a plurality of discs interposed betweenpairs of the discs mounted on the shaft, the discs on the shaft and onthe casing being submerged in viscous fluid contained within the casing,said discs and viscous fluid forming a fluid couple between the shaftand the casing, and an inertial member carried by the casing wherebyrotation of the servo-motor shaft is dampened by the drag of the viscousfluid between the faces of the discs and the inertia of the inertialmember.

4. The combination as recited in claim 3 wherein means operativelyconnected to the servo-motor maintains the inertial member stationarywhereby the rotation of the servo-notor shaft is dampened only by thedrag of the viscous fluid between the faces of the discs.

5. In a servo motor mechanism for a graphic plotter or the like, thecombination comprising a rotatable shaft, a casi-ng rotatably mounted onsaid shaft, viscous damping means in said casing for viscous damping fsaid shaft during rotation, inertial damping means operatively mountedon said casing whereby said shaft is provided with viscous-coupledinertial damping, and means movable between latching positions relativeto said inertial damping means, said movable means in one latchingposition locking said casing against rotation whereby said shaft isprovided with viscous damping, said movable means in another latchingposition permitting rotation of said casing whereby said shaft isprovided with viscouscoupled inertial damping, and means operativelyengaging said movable means for moving the same between latchingpositions.

6. The combination as recited in claim 5 wherein said movable meanscomprises clamping elements operating on said inertial damping means.

7. The combination as recited in claim 6 wherein said clamping elementsare biased to the one latching position t3 and said operatively engagingmeans comprises a slidable key to move said clamping elements againsttheir bias to the `other latching posit-ion.

S. ln a servo-motor mechanism for a recorder or the like, thecombination comprising a rotatable shaft, a casing rotatably mounted onsaid shaft and containing a viscous iuid, disc means xed to said casingand being disposed in said iiuid, cooperating disc means secured to saidshaft and being disposed in interface relationship with the casing discmeans to form viscous damping means for said shaft, an inertial elementfixed to said casing for rotation therewith to form inertial dampingmeans for said shaft, latching elements movable into engagement withsaid inertial element to lock the same against rotation whereby :saidshaft is provided with viscous damping, said latching elements beingmovable out of engagement with said inertial element to permit rotationthereof whereby said shaft is provided with combined viscous andinertial damping, and selector means operatively engaging said latchingelements for selectively moving the same relative to isaid inertialelement.

9. The combination as recited in claim 8 wherein spring means biasessaid latching elements into engagement with said inential element, andsaid selector means comprises a latching key for moving said latchingelements against the bias of said spring means and out of engagementwith said inertial element.

10. In a servo-motor mechanism for a graphic plotter or the like, thecombination comprising a shaft rotatable about a longitudinal axis, acasing rotatably mounted on said shaft and containing a viscous fluid, aplurality of discs fixed to said casing and being immersed in saidliuid, a similar plurality of discs secured to said shaft and beingdisposed in interface relationship with the casing discs to form a fluidcoupling whereby rotation of said shaft effects rotation of said casing,an inertial element fixed to said casing for rotation therewith wherebysaid shaft is provided with combined viscous and inertial damping, ahousing enclosing said inertial element and said casing, an end platesecured to said housing and being disposed transversely to the axis ofsaid shaft, a pair of latching elements slidably disposed on said plateon opposite sides of said axis, a latch bar on each of said latchingelements disposed adjacent said inertial element, spring means mountedin tension between said latching elements and biasing said latch bars inclamping engagement with said inertial element, a latch key slidablymounted on said plate and being operable to slide said latching elementsagainst the bias of said spring means whereby said latch bars are movedout of clamping engagement with said inertial element, and camming meansoperatively disposed between said latch key and said latching elementsto facilitate manual operation of -said latch key.

References Cited in the tile of this patent UNITED STATES PATENTS2,417,282 Wheeler Mar. l1, 1947 2,454,980 Sobell Nov. 30, 1948 3,054,304lJursik et al. Sept. 18, 1962

1. IN A SERVO-MOTOR MECHANISM, THE COMBINATION COMPRISING A ROTATABLESHAFT, OUTPUT MEANS CONNECTED TO SAID SHAFT AND ADAPTED TO RECORD DATAFED TO A SERVO MOTOR, A CASING ROTATABLY CONNECTED TO SAID SHAFT ANDCONTAINING A VOLUME OF FLUID, FLUID DAMPING MEANS SECURED TO SAID SHAFTAND EXTENDING INTO SAID CASING FOR VISCOUS DAMPING OF SAID SHAFT DURINGITS ROTATION, AND AN INERTIAL ELEMENT SECURED TO SAID CASING FORROTATION THEREWITH WHEREBY VISCOUS DAMPING OF SAID SHAFT IS COMBINEDWITH INERTIAL DAMPING OF SAID SHAFT DURING ROTATION THEREOF.